Paper drying hood



April 6, 1965 M. D. JEPSON ETAL 3,175,411

PAPER DRYING HOOD Filed Sept. 26, 1960 8 Sheets-Sheet 1 FIG. 7.

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April 1965 M. D. JEPSON ETAL 3,176,411

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April 1965 M. D. JEPSON ETAL 3,176,411

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PAPER DRYING HOOD Filed Sept. 26, 1960 8 Sheets-Sheet 7 F IG. 5.

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April 6, 1965 Filed Sept. 26, 1960 M. D. JEPSON ETAL 3,176,411

PAPER DRYING HOOD 8 Sheets-Sheet 8 X INVENTORS mm @W 472/ W W 952 4 14a.BY aldwm) W ZZZM FIG. 9.

United States Patent 3,176,411 PAPER DRYING HOOD Michael Denis Jepson,Ilkley, and George Flaxman Underhay, Weybridge, England, assignors toThe Bowater Research and Development Company Limited, London, England, acompany of the United Kingdom- Filed Sept. 26, 1960, Ser. No. 58,265Claims priority, application Great Britain, Sept. 2, 1960, 30,426/ 60 7Claims. Cl. 34-422) The present invention relates to papermakingmachinery and more particularly to drying sections of papermakingmachines.

It is the principal object of the invention to provide an improvedmethod and means for evaporating the moisture from the web and forincreasing the rate of drying in papermaking machines.

In conventional machines the distribution of moisture in the web issomewhat uneven and in wide machines this may be very marked. Forexample, if paper is taken from the machine at an average moisturecontent of 6% it is not uncommon to find that the actual moisturecontent transversely of the web varies from 4% at one part to 8% atanother part at the dry end of the drying section. Thus, if it werenecessary not to have a moisture content of more than 6% at any part inthe paper some of the paper would have to be overdried to reduce themoisture content of those parts of the paper having 8% of moisture downto 6% and the parts having 4% would be further over-dried. Moreover, thewhole process of drying might have to be slowed up to allow the wetterportions to be dried down to the maximum permissible moisture content.

It is a further object of the present invention to provide a control ofthe moisture distribution across the paper web.

According to one aspect of the present invention, in a papermakingprocess wherein the web is dried by entrainment around one or moreheated drying cylinders and by directing gaseous drying medium directlyon to the outer surface of the web about the drying cylinder in suchmanner that evaporation of moisture from the web surface andtransference of heat from the drying cylinder are enhanced at dryingzones arranged transversely of the web, individual control of the dryingrate in each zone is achieved by adjustment of the velocity of thedrying medium directed onto the web at that zone or the temperature ofthe drying medium so directed or the humidity of the drying medium sodirected or any combination of two or all of such adjustments, thegaseous medium, after flowing over and away from the outer surface ofthe web being caused to flow transversely of the web and then to flow ina direction away from the surface of the cylinder.

By the use of the invention it is possible to control the rate of dryingtransversely of the web to a degree sufficient to ensure that the webmay be dried down to an overall pre-determined moisture content withoutany part of the paper being overdried or without any remoistening orconditioning of the paper after drying being necessary.

In order to avoid any tendency for the web to lift from the surface ofthe drying cylinder the velocity of the gaseous medium flowing away fromthe outer surface of the web is preferably substantially lower than thevelocity of the gaseous drying medium directed onto the outer surface3,176,411 Patented Apr. 6, 1965 a drying hood for a drying cylinder of apaper-making machine comprises a plurality of pressure chambers disposedin side by side relationship transversely of the direction of papertravel, each pressure chamber having an arcuate face adapted to theperiphery of the drying cylinder and containing nozzle orifices for thedirection of gaseous drying medium onto a web of paper on the peripheryof said drying cylinder, and means for supplying gaseous drying mediumto said pressure chambers and for enabling the drying rate achieved bythe drying medium directed from the nozzle orifices of each pressurechamber to be individually controlled, by adjustment of the humidity ofthe drying medium supplied to each pressure chamber, or the temperatureof the drying medium supplied to each pressure chamber, or the rate ofsupply of drying medium to each pressure chamber, or any combination oftwo or all of such adjustments, and exhaust passageways spaced aparttransversely of the direction of paper travel by which the gaseousmedium after flowing over and away from the surface of the web can flowin a direction away from the periphery of the drying cylinder.

According to a further feature of the present invention, a drying hoodfor a drying cylinder of a drying section of a papermaking machinecomprises a manifold, fan means for supplying gaseous medium to saidmanifold, heating means for heating the said gaseous medium, a pluralityof pressure chambers disposed in side-by-side relationship transverselyof the direction of paper travel, each pressure chamber communicatingwith said manifold for receiving heated gaseous medium therefrom andhaving an arcuate face adapted to the periphery of the drying cylinderand containing nozzle orifices for the direction of heated gaseousmedium onto a web of paper on the periphery of said drying cylinder soas to hold the web in close non-adhesive contact with the cylinder,valve means for individually controlling the flow of gaseous medium fromsaid manifold to each pressure chamber, and exhaust passageways spacedapart transversely of the direction of paper travel by which the gaseousmedium after flowing over and away from the surface of the web can flowin a direction away from the periphery of the drying cylinder.

Preferably the pressure chambers are spaced-apart and the spaces betweenthem provide at least some of the exhaust passageways.

Preferably the manifold lies directly adjacent said pressure chambersand on the opposite side thereof to their arcuate faces and said valvemeans conveniently comprises shutters controlling ports in a wallbetween the manifold and the pressure chambers.

Since the gaseous medium must be brought into direct contact with theweb entrained around the cylinder no dryer felt is employed. Theinvention is applicable to any type of drying section and can be usedwith machines employing a number of small cylinders, a single largecylinder such as is generally used for the production of glazed orcreped paper, or a combination of both large and small cylinders. In thecase of a multi-cylinder drying section when the web is maintained innon-adhesive contact with the cylinders, the necessary pressure tomaintain contact, and which, in conventional machines is produced by thedryer felts, is generated by the pressure of the gaseous medium directedonto the web or any longitudinal tension which may be applied to the webor both.

In a preferred arrangement the drying hood has an outer casing forcollecting spent gaseous medium flowing away from the periphery of thedrying cylinder, the fan means communicating by its inlet side with theinterior of said casing whereby to re-supply spent gaseous medium tosaid manifold. The preferred drying medium is predominantly air, but itwill be appreciated that in general a proportion of water vapour fromthe web is present and is beneath the exhaust openings.

. I a r to avoid Saturation of the drying generally made for exhaustingsome of the spent air thecasing and supplying fresh make-up air thereto.The

medium provision is from;

pressure chambers,;the manifold and the fan means can.

all'be disposed withinthe outer casing with the heating;

means situated at the entry or entries to a supplychamber which isformed between the manifold and the wall of The inlet of the fan meanscan thus lie within the supply'chamberand the outlet.

the casing opposite thereto.

within the manifold. This is most conveniently achieved if the fan meanscomprises at least one axial flow fan driven by a motor which maybesituated outside the cas- V from'a common manifold 42.

ing. In the preferred arrangement the arcuate faces of the pressurechambers are contiguous and exhaust channels extendinglongitudinally ofthe drying cylinder but at the opposite side of the arcuate faces to thecylinder communicate with'the-exhaust passageways, said arcuate I faceshaving exhaust openings to permit thespent 3.11 to flow into the exhaustchannels.

The total area of the exhaust openings is preferably-subst-antiallygreater than that of'the nozzle orifices so that the velocity of the airflowing away from the cylinder is substantially less than the velocityof the drying air d1- 7 be necessary thata positive :pressure bemaintained' beneath the exhaust openings and even aslrght negativepressure may not, in certain circumstances, bGdlSfiKlVQIltageous." v V IItis generally preferred however that'the lowestpressure of the gaseousmedium under the'hood is sufficient" to avoidthe uncontrolled inflow of,air at ambient condi-. tions from outside the hood under itsbottom'edges.

The invention will be further. described by way of example "withreference to the accompanying drawings, in

which:

FIG. 1 is a diagrammatic side elevation oflpart of-a.

multi-cylinder drying section of a paper making machine incorporating adryinghood constructed according to the present invention; a i FIG. 2 isa front elevation of the drying hood of FIG. 1; FIGS is a cross sectionon the line III-III'of FIG. 2

. to a larger scale, the section line III- 1H also being in dicated inFIG. 4;.

FIG. 4 is a section on, 7 section line IV-IV also being indicated inFIG. .5;

FIG. 5 is'a detailed section on the line V-V of FIG. 4;.

FIG. 6 ,is a detailed cross section on the line VI VI of FIG. 3 to astill larger scale, the section line VI VI also being indicated in FIG.5; I I FIG. 7 is an enlarged detail of the section shown 1n FIG. 4forcomparison with. FIG. 6; v

FIG. 8 is a section on the line ;VIII--VIII of FIG. 3,

the nae rv-i-rv ofFIG. s, the

"T he drying hood 2% contains six pressure chambers 30,. 32, 34, 36,38and deployed axially of the cylinder in the positions indicated bydotted lines in FIG. 2. The

'- pressure chambers are individually supplied with gaseous dryingmedium, which'in the embodiment shown is air,

FIGS. 3 to 8 show the construction of the drying hood in more detail.Referring to FIG. 4, the pressure chambers 38 and 40 are spaced apart sothat their longitudinal partition'walls 39 and 41 define an exhaustpassageway 44 by which spent air can flow in adirection away from thesurface of the cylinder 22. ,Allthe other pressure chambers are likewisespaced apart: I

- 'As can be seen from FIGS. 3 to 7, a series of flow passage meansformed as channels 46 extend along the cylin-. der 22,behind'aperforated arcuate bottom wall' or face 48 of eachpressurechamber, the arcuate faces substantially'conforming to theperiphery of the cylinder in ra-' dially outwardly spaced'relation tothelatter; Drying air in thepressure chamber 38 :has access to nozzleorifices '54 in the form of holes arranged in the arcuate face 48 forthe projection or air towards the webof paper on the sur-'- face of thecylinder 22.. This is indicated in FIGS. 3 and 6 by arrows 52. I I IAlthough the following description refers for the most part to thepressure chambers 38 and 40, it will be. appre,

V ciated that all thepres'sure chambers 30, 32, 34,36, 33

. and 40 are of similar construction.

i As can be seen in FIGS. 6 and 7,.the arcuate faces of the pressurechambers are contiguous although the press surechamber walls 39 and 41are spaced apart. The chan- 1 nels 46 extend the full length ofthecontiguous arcuate "faces 48 but are open to the exhaust passageway44 attheir facesopposite the arcuate faces 48, as can be seen in FIG. 7; 'Thegaps betweenthefchannels provide access to. the'ndz-zle orifices for theairin the pressure chambers and are isolated from the exhaustpassageway44by plates 7 3 4'7 1 as can be seen in FIGS. 5 and 6 Intercommunicationbetween the'pressure chambers along the gaps between ,thechannels 46 isprevented by plates 54 (see FIG. 6).

fThe flow passage channels 46 lead spent air flowing 7 from the spacebetween'th'e arcuate faces 48 and the cylin- V der through larger sizeopenings-56 to the exhaust passageway 44, mean he se'en from FIG; 4.Although only a few 'no'zzle orifices 50'and exhaust openings 56 areshown, it will be appreciated that'these :extend over subf stantiallythewhole of the arcuate faces 48of thepressure the sectionline VIII-VIIIalso being'indicated in FIG. '4;

' FIG. 9 is a cross section similar to that shown inFIG.

4, but of another embodiment of drying hood according, l

to the invention; and I FIG. 10 is a detail section on the line X-eXiofFIG. 9.

Referringnow to th drawings, and'm'ore particularly to FIGS."1 and 2,adrying hood 20 constructed accord ng to the present invention isdisposed about anv upper cylinder 22 of faImulti-cylinder drying sectionof a paper makk 24 to be dried passes al-,

ing machine; A web of, paper chambers. The path of the spent airisindicated by arrows 58 in FIGS. 3, 4, 5 and 7. Ascan be seen from thesefigures, the spent air,'after issuing through the nozzle orifices 50,flows only to a limited extent circumferentially of the cylinder before.flowing away from the cylinder through the exhaust openings 56. Thespent air then flows transversely of the web along the channels 46 tothe exhaust passageway 44 or one of the other'exhaust'passagewaysbetween the pressure chambers or to an end exhaust passageway '45 (FIG.4), whereupon it can fiow freely through gaps 45b (FIGURE 5) inthetransverse walls 450: and away from the drying cylinder 22.1 The exhaustpassageways L are circumferentially coextensive about the cylinder withthepressure chambers, and'are spaced apart axially'of the cylinder. 7

.The drying hood'20 is provided with an outer casing. 60v havingsidewalls 62 transverse to the direction of movement of the'web, endwalls 64 longitudinal tothe direction of movement, ofythe' web and'a top'wall66 j formed of heat insulating panelling (see FIGS. '3 and 4).

Two spaced inner walls 45a, transverse to the direction of f ,t-raveliofthe web, extend from'the'bottom wall 48 to the manifold 42, one at eachside of the arcuate part of the bottom wall 48 Thetransverse walls 45aare spaced from ternately round cylinders in :an upper row a cylindersin alower row, those 1n thei'upperrow, other than the by 26 and thosein.the lower cylinder 22, being indicated row by 28 in FIG. I. I I

the respectively adjacent outer transverse walls 62 to define "the endexhaust passageways 45. A supply chamber 68 1 (FIG. 3) is formed betweenthe manifold 42 and the top wall 66 of the casinggand main fans 70 arearranged between the supply chamber 68 and the manifold 42. Spentto themanifold 42 by the main fans 70, which are driven by motor 72. The spentair flowing into the supply chamber 68, passes through heaters 74 in theform of a plurality of finned steam pipes 76, supplied with steam thoughvinlets-78, and having steam outlets 80.

The mainfans 70 are axial flow fans having their inlets 82 disposeddirectly in the supply chamber 68 and their outlets 84, having adiffuser 86, directly within the manifold 42. This construction avoidsthe use of any ducting between the supply chamber and the manifold 42and leads to a compact space-saving arrangement.

Each of the pressure chambers is individually supplied with air from themanifold 42. As can be seen in FIGS. 3 and 4, the top Wall 88 of eachpressure chamber is intermediate each pressure chamber and a top innerwall 42a. The inner transverse walls 45a, together with the I topinnerwall 42a and the intermediate wall 88, define the manifold 42. Thetop wall' 88, which forms the bottom wall of the manifold 42, isprovided with ports 90 to permit the air to flow into the pressurechambers. The ports 90 are controlled by shutters 92, each of which isindividually slidable by means of a Bowden cable 94 to enable individualadjustment of the flow through the ports 90 to be made.

As can be seen more clearly in FIG. 8, each of the ports 90 is cuspshaped and in particular comes to a point at one end to enable a finecontrol of the quantity of air flowing from the manifold 42 to eachpressure chamber to be obtained. For ease of manipulating the shutters,the shutters are provided with runners 96 which run in channels 98, ascan be seen in FIGS. 4 and 8.

It will be appreciated that the drying air is circulated along asubstantially enclosed endless path, which comprises the manifold 42,one of the pressure chambers, the nozzle orifices 50, the exhaustopenings 56, the flow passage channels 46, one of the exhaustpassageways and the supply chamber 68 whence it is re fed to themanifold 42 by the main fans 70.

In order to prevent the drying air so circulated becoming saturatedwith, water vapour, some of the air and evaporated water, so circulatedis withdrawn through exhaust ducts 100 and fresh air is supplied throughducts 102 (see FIGS. 1 to 5). As can be seen more clearly from FIGS. 1and 2, there are two exhaust ducts 100 which, are joined into a singleduct 101, within which, is disposed an exhaust fan 104, of the axialflow type, driven by amotor 106 (indicated diagrammatically in brokenlines in FIG. 2). The exhaust fan 104 withdraws spent air from withinthe casing. 60 and the spent air is discharged,for example, into a flue(not shown). The quantity of spent air withdrawn is controlled by adamper 112. The make-up air ducts 102, which are also two in number, aresupplied, from a common duct 103, within which there, is disposed afresh-air fan 108, also of the axial flow type, driven by a, motor 110(indicated diagrammatically in broken lines in FIG. 1). The fresh-airfan 1'08- draws fresh air in from the atmosphere through a filter 114.and supplies such fresh air to the supply chamber. The quantity of freshor make-up, air is controlled by adamper 116 (FIG. 2).

Cooling air for the motors 72 driving the main fans 70 is also suppliedby the fresh-air fan 108. For this purpose ducts 118 leading-to themotors 72, are also connected to the common duct 103, as shown in FIG.2. It can conveniently be arranged that cooling air after cooling themotors 72, flows through the fan centres and is discharged just beforethe fan rotor'blades of the main fans so as to mix with the drying airbeing circulated. If desired, the make-up air can be heated, for exampleby steam or electrical heaters (not shown). If the make-up air is alsoused to cool the motors 72 as shown, then the temperature to which suchair is heated is limited by the temperature rating of the motors 72.This temperature may, for example, be 160 F. If it is desired to heatthe make-up air to a higher temperature, then a separate supply ofcooling air for the motors 72 is preferred. It is not essential that themake-up air be heated before supplying to the supply chamber; themake-up air can obtain heat by admixture with the air beingcirculatedthrough the heaters 74.

The rate of supply of drying air to each of the pressure chambers can beindividually controlled, thereby enabling the drying rate at six zonescontiguously arranged transversely of the web to be separatelycontrolled. The- Bowden cables 94 attached to the shutters 92 (FIGS. 3and 8) lead to a control panel 128 (FIG. 1) fitted with cranks orhandles 130 for adjusting the shutters. The control panel 128 also hasfurther handles 132 operating Bowden cables 134, which control thedampers 112 and 116 in the exhaust air and makeup air ducts (FIG. 2).

The shutters are adjusted in order to obtain as even a moisturedistribution, transversely of the finished web, as possible. Should themoisture profile transversely of the web vary during operation of thepaper making machine, for example due to uneven wear of the calender orpress rolls, then appropriate corrective action may betaken at thecontrol panel 128.

In order to provide access to the surface of the cylinder 22, forexample when threading the web through the machine, or when removingtorn paper should a break occur in the web, the drying hood 20 ispivoted to a fnamework 120 situated at one end of the cylinder 22 and toa piston rod 122 of a pneumatic piston and cylinder mechanism 124situated at the other end of the cylinder 22, as can be seen in FIGS. 1and 2. The upper end of the mechanism 124 is mounted on the framework126. The make-up air duct 103 is provided with a flexible portion 128 toavoid having to disconnect this duct when lifting the drying hood awayfrom the surface of the cylinder.

The drying cylinders 22, 26 and 28 are internally steamheated in theconventional manner, the means for this purpose being omitted from thedrawings for the sake of clarity.

More than one of the cylinders of the upper row may be provided withdrying hoods according to the present invention, if so desired. Whereadjacent cylinders in the same row have such drying hoods then thesupply chambers, possibly the manifold and possibly also the pressurechambers, as well as the outer casing, may be arranged to be common tosaid adjacent cylinders. Moreover, drying hoods according to the presentinvention may also be adapted to the drying cylinders of the lower row.In order to increase the drying capacityof the drying section, a largenumber of drying hoods may be used. In this case it is not necesary thatall the hoods be provided with shutters for individually controlling thedrying rate transversely of the Web, but it is desirable that they be soprovided so that a substantially uniform moisture profile may beobtained through as large a part of the drying section as possible. Thusa uniform moisture profile transversely of the web may be obtainedsubstantially throughout the drying section. This reduces the risk ofwrinkles developing in the web.

A drying hood according to the present invention can be fitted to anexisting machine in order to improve the uniformity of the moisturecontent of the finished web and in order to increase the capacity of thedrying section.

It is at present common practice to over-dry the web in the dryingsection of -a paper making machine and then to subsequently re-moistenthe web in a separate operation, so that the finished product will havea moisture content which is in keeping with the humidity of thesurcylinder.

rounding atmosphere, in order to obtain a. moisture distribution whichis as uniform as possible throughout the web. By providinga drying hoodaccording to the in ventionlover at leastone of the cylindersof a multicylinder drying section, the "web can be dried to a substantiallyuniform wetness in keeping with thehurnidity In the embodiment of thedrying hood shown, the total of the surrounding'atmosphere, thusavoidingthe nec'es--f Y sure chambers, by means not shown. The pressurechamhere may also be provided with thermometers, if desired.

The humidity of the drying air being circulated is controlled by thedampers 112 and 11s (FIG. 2), and samples of the spent air flowingthrough the exhaust duct 101 then-there-would be arisk of-the web beinglifted from may bejtaken'for the purpose of assessing thelmoisture"content of the "drying air being circulated. I 3 I In operation, heatistransferred to theweb' on the drying cylinder 22 not only from thedrying cylinder but also from the heated air directed onto the web.Morecrossasectional area of the exhaust openings is approximatelytwenty-eight times thetotal cross-sectional area of the nozzle orifices.;Thus the velocity of the spent air flowing awayfrom the web 'through'the exhaust openings is very muchlower than the velocityofthe airflowing towards the web through the nozzle orifices. Moreover,

I there issome resistance to the flow of the spent air flowing throughthe exhaust channels and through, the exhaust over, the rate of heattransfer from the drying cylinder-to the web is enhanced by'bl'owing airon to the web for by taking away the evaporated'moisture in th'cspcntair the rate ofevaporation is increased thereby increa'singthetemperature difierencebetween theweb land thedrying Although a to-amulti-cylinder drying section of a paper-making maf dryinghoodaccording to-the present chine it can also be applied to'a paper-makingmachine having one large drying cylinder only, whether that cylinder isan M.G. cylinder or not; -Where an-M.G. cylinder is'used the" webusually pressed intoadhesiye; contact with the cylinder; Where anunpolished cylinder, whether of large or small diameter, is used the webis held close but non-adhesive contact with'thecylinder'. In

this latter case, the drying :air issuing from the nozzle.

orifices of a drying hood according to the present invention creates aforce acting on the outer surface of the web, thusQat least assisting inmaintaining theweb in close'but non-adhesive contact with the cylinder.Where passageways, so that a slight positive pressure may be stillmaintained beneath the exhaust openings. 1

It will be appreciated that the provision of a large number'of exhaustchannelsat fairly. closely spaced intervals enables the spent air to beremoved fromthe surface ofthe web without the surface of the webbeingpresented to large openings extending transversely of the web. If theweb were exposed to such large openings,

the s'urface'of-the drying cylinder beneath such openings,

" and .be'ing drawn into. the machinery within the drying hood. In thedrying hood of thepresent invention there are large exhaust openings,namely at the exhaust pas sageways', but theseextend circumferentiallyof thedrying cylinder, i.e'. longitudinally of the web, and they com-'rnunicate witlr' theexhaust channclsand not directly with the exposedsurface ,of the web. Thus the risk of the web being broken. and drawn'intothe exhaust passageways isfreducedto'aminimum.

' The perforated arcuate faces of the pressure chambers present asubstantially smooth surface to the web abou'tthe drying cylinder sothat should a break-occur in the web there is little risk of the brokenweb being caught up o'nthe drying hood and damaging the hood.

It will be appreciated-that although the drying hood in'gs.Princip'alparts which are like those of the ema paper-makingmachine-liasa drying section with an M.G. cylinder and one or morepro-drying cylindersa drying hood according to the present invention maybe applied to some or all of the pro-drying cylinders. It'is envisagedfurther-more that drying hoods according to the present invention can beapplied to, drying sections hav-' ing few, large diameter dryingcylinders compared with. conventional multi-cylinder drying sectionshaving a large numberof .small,.e.g. 5 ft.,diameter, drying cylinders.

In a multi-cylinder. drying section, the web is main;

bodimentof FIGS. '1 to 8 are indicated by like reference numerals; Theembodiment of FIGS. 9 and 10 differ from that of the previousembodimentfprin'cipally in i that the pressure chambers, of which 238and 240 are seenin the drawings, instead of being spaced apart, adjoinone another. Exhaust passageways 244, which extend circumferentially ofthe drying cylinder 22, are arranged within the pressure chambersthemselves. The arrows 258- indicatethepassage-of spent air-fromthesurface of the web through the exhaustopenings 56, and

- the flow'passagechannels 46 'and exhaustpassageways 45 and 244 throughgaps 455 into the-casing 60. The

tained in closev but non-adhesive contact with the drying cylinders, inorder topermit amaximum rate "of heat transfer from the cylinder. to theweb. If the Web is sufiia ciently strong, then maintain such contact, 7However, if -the' Web is very weak, then it is usual to provide felts inorder to press the web into close non-adhesive contact with the dryingcylinders. The felts, however, hinder the flow of moisture awaybetween'the channe1s46 to completely the tension in the web canbe. usedtO' 7 sure "chambers from one another.

from the Web as it is dried. .With the use of a drying hood according tothe present invention the drying air issuing from the nozzleorifices'creates aforce acting on the outer surface of the web to'holdthe web in close nonx adhesive contact the drying cylinder asdisclosedin United States Patent No. 2,919,495.. -Drying hoods'according to the present invention obviate thenecessity for pressurechambers 238' and 240 are in etfect separated by a longitudinalpartition 239, which extendsat 241 isolate the pres-It'willbe-seenthat,in'the' embodiment of FIGS. 9 and 10-, the spent air,immediately after direction towards the surface of the web,'first flowsonly to a limited eX- tent circumferentially of the drying cylinder,then through the exhaust openings Sdinto the channels 46 andsubsequently transversely'of. the web into the exhaust passageways 244and 45, wherein'it'can how in a, direction away, from the surface ofthe-drying cylinder. The manner in'which the 'spentair is led away fromthe surface of-the' rcylinder is therefore substantially thesarne asthat in'the embodiment of FIGS. 1 to 8. r

felts, except possibly at the wettest part of the dryingsection.However, it is. necessary that the risk of the web.

lifting from-the surface of the cylinder when beneath the exhaustopenings be reduced to a minimum. To end the total cros's-sectionalareaof the exhaust opcning's is made very much larger thanthetotalcross-sectional are-a dof the nozzle orifices, preferably at leastsixteen i Although the embodiments of the inventlon shown in thedrawings employ steam heaters, other :forms of heating means could beemployed such as. electrical heating elements and] gas and oil burnerswhich may heat the circulated air either; indirectly or by admixtureoftheir products of combustion withthe circulated air.

9 In the embodiment of drying hood illustrated in FIGS. 1 and 2 of thedrawings, access to the surface of the drying cylinder is obtained bypivoting the hood about one end. It may, however, be preferable,according to the design of the frame of the drying section to which thehood is applied, to arrange for the hood to be liftable vertically, forexample by four hydraulic or pneumatic piston and cylinder mechanisms orscrew jacks arranged at its corners. The pneumatic piston and cylindermechanism illustrated in FIGS. 1 and 2 may be replaced by a hydraulicpiston and cylinder mechanism so desired.

7 In the illustrated embodiments of the invention, the shutterscontrolling the ports between the common manifold and the individualpressure chambers are manually operable using Bowden cables. However,the shutters could be operated by air or hydraulic cylinders or byscrewed rods on each of which a nut is rotatable by "means of an air orelectric motor.

It is envisaged that the moisture profile transversely of the finishedweb may be controlled automatically.

For this purpose moisture content sensing shoes, corresponding in numberand transverse positions to the numher and transverse positions of thepressure chambers,

,may be arranged to meter the moisture content of the Web leaving thedrying section, each of themoisture content sensing shoes beingconnected electrically or otherwise so as to control the shutterassociated with the corresponding pressure chamber. Alternatively asingle I moisture content sensing shoe may be arranged to traweb in sixgroups of three, the groups being spaced from one another to providefive exhaust passageways between adjacent pressure chambers. Such astructure is achieved by dividing each pressure chamber of the dryinghood illustrated in FIGS. 1 to 8 into three, each one of which has itsown shutter controlling the supply of heated air thereto from the commonmanifold. It is desirable that the spent air should flow through theexhaust channels with a significant velocity, the consequent pressuredrop in the exhaust channels being used to maintain a slight positivepressure beneath the exhaust openings in the arcuate faces of thepressure chambers. If too many exhaust passageways were provided theywould be a comparatively short distance apart so that the air velocityin the exhaust channels, which would be correspondingly shorter, wouldbe negligible, leading to a negligible pressure drop in the exhaustchannels which could not be used to maintain a positive pressure beneaththe exhaust openings. Moreover, the provision of a comparatively fewexhaust passageways transverse of the Web when a large number ofpressure chambers is employed leads to a simplification in construction.

It is possible to obtain pressures ranging from 4 ins. to 16 ins. watergauge (measured at 60 F.) in the manifolds of the illustratedembodiments of the invention. Thus the pressure in each of the pressurechambers may be varied from zero to 16 ins. water gauge. By using morepowerful fans or a greater number of fans higher pressures are, ofcourse, possible. A static positive pressure (with respect toatmosphere) of from 0.1 in to 1 in. water gauge (measured at 60 F.) isobtainable immediately beneath the exhaust openings in the perforatedarcuate faces of the pressure chambers.

What is claimed is: l. A drying hood for a drying cylinder of a. machineI for drying sheet material in continuous lengths to be entrained aboutsaid cylinder, comprising a casing having longitudinal walls, transversewalls, a top wall and a bottom wall, said bottom wall being at least inpart of exteriorly concave arcuate shape adapted to the periphery Of thedrying cylinder and having its axis substantially parallel to saidtransverse walls; a manifold within said casing, a supply chamber beingdefined between said top wall and said manifold; heating means disposedin said supply chamber for heating gaseous medium therein; fan meanshoused within said casing and having its inlet in said supply chamberand its outlet within said manifold for supplying heated gaseous mediumfrom said supply chamber to within said manifold; two transversepartitions parallel respectively to the transverse walls and extendingfrom said bottom wall to said manifold one at each side of said arcuatepart of said bottom wall defining a path for return flow of exhaust gasto the supply chamber; longitudinal partitions extending between saidtransverse partitions to define a plurality of pressure chambers betweenthe bottom of the manifold and the arcuate surface, and a plurality ofexhaust passageways coextensive with the pressure chambers about theperiphery of the cylinder, the face of said manifold facing said bottomwell being provided with ports for the flow of heated gaseous mediumfrom the interior of said manifold to each of said pressure chambers;shutters for closing said ports to a variable extent, each of saidshutters being individual to one of said pressure chambers; and meansfor individually adjusting said shutters from without said casing, saidarcuate part of said bottom wall being apertured for the direction ofgaseous medium from said pressure chambers on to a Web of paper on saiddrying cylinder and further apertured to provde access to said exhaustpassageways for gaseous medium flowing over and away from the outersurface of said web on said cylinder and said exhaust passagewayscommunicating through said transverse partitions with said supplychamber for the return to said supply chamber of gaseous medium receivedin said exhaust passageways.

2. In drying apparatus including a drying cylinder about which sheetmaterial in continuous lengths to be dried is entrained, the combinationcomprising a plurality of pressure chambers deployed axially of thecylinder, said pressure chambers having axially aligned arcuate facessubstantially conforming to the periphery of the cylinder in radiallyoutwardly spaced relation thereto and having nozzle orifices fordirecting gaseous drying medium from the pressure chambers onto sheetmaterial entrained about said cylinder; exhaust passagewayscircumferentially coextensive about said cylinder with said pressurechambers and spaced apart axially of said cylinder, each exhaustpassageway being separated from the next thereto by at least one of saidpressure chambers; means communicating through said arcuate faces fordirecting said gaseous medium axially of said cylinder to said exhaustpassageways after said gaseous medium has flowed over and away from thesurface of said sheet material; means for supply ing gaseous dryingmedium to said pressure chambers; and means for enabling the drying rateof the sheet material achieved by said gaseous drying medium directedfrom each said pressure chamber to be independently controlled.

3. In drying apparatus including a drying cylinder about which sheetmaterial in continuous lengths to be dried is entrained, the combinationcomprising a plurality of pressure chambers deployed axially of thecylinder, said pressure chambers having axially aligned arcuate facessubstantially conforming to the periphery of the cylinder in radiallyoutwardly spaced relation thereto and having nozzle orifices fordirecting gaseous drying medium from the pressure chambers onto sheetmaterial entrained about said cylinder; exhaust passagewayscircumferentially coextensive about said cylinder with said pressurechambers and spaced apart axially of said cylinder; flow passage meansradially outwardly beyond said arcuate faces extending axially of saidcylinder and comalt e 11 municating with said exhaust passagewayasaidflow' paS? sage means also communicating through saidi arcuate i faceswith the spaces between said arcuatei faces andts'aid' cylinder wherebygaseous medium'whichhas flowed over I and away from the surface of'saidsheet material will flow outwardly through said arcuate ,faces into saidflow pas sage means and will then flow axially of said cylinder withinsaid flow'passage means to said exhaust passageways; means for supplyinggaseous drying medium to, said pressure chambers; and means for.enabling 'the drying" I rate of the sheet material achieved by saidgaseous drying rnediumdirected from each said pressure chamber to beindependently controlled.

an enclosing casing having a bottom Wall' which provides saidpressuretcharnber-arcuate faces; twospaoed apart 4. Drying r-apparatusaccording to claim "3 in which said exhaust passageways arev within,said pressure,

chambers. i

5. Drying apparatus according to claim} comprising an enclosing casinghaving a bottom wall which-provides saidpressure chamber arcuate faces;an intermediate wall spaced from said bottom Wall; two spaced aparttransk verse walls parallel to the cylinder'axis on opposite sidesthereof and extending between said intermediate and bottom Walls, saidintermediate 'wall dividing the casing in;

terior into a lower space bounded by said bottom wall;

said transverse walls, and said' inte'rmediate' wall, and a collectingspace; a plurality of sp'aced apart partitions inner transverse wallsparallel'to the cylinder axis and onopposite sides thereof; anintermediate wall spaced irom said bottom wall and extending from oneofsaid transverse walls. tolthe other; a plurality of spaced apartpartitions between said transverse walls extending parallel tothedirection of motion of sheet material entrained about said cylinder,said inner transverse walls, said bottom wall; said intermediatewall andsaid partitions defining-said pressure chambers andsaid exhaustpassageways,

saidmeans for enabling the drying rate of the sheet ma- :te'rial to beindependently controlled comprising separate independently operableinletmeans between said manitold and the respective pressure chambers;

7. Drying apparatus according to claim 6 in which f independentlyoperable inlet tmeans comprises cusp respectively extending from one ofsaid transverse walls to the other in the direction'ofrnotion ofsheetmaterial entrained about said cylinder, said transverse walls, saidbottom wall, said intermediate wall and said partitions defining said'pressure chambers and said exhaust passageways, one of saidtintermediateand transverse walls-having a pluralityof ports separately providingcommunica tion between said collecting space and the respective pressurechambers and at least one other of, said intermediate and transversewalls having gaps' providingv communication between said exhaustpassageways and said collect ing space, said meansfor supplying gaseousdrying me dium to said pressure chambers including a heater within saidcasing, and said means for enabling the drying rate of the sheetmaterial to be controlled comprising means within said casing butoperable from the exteriorthere'of for controlling the flow of dryingmedium from said collecting space through said ports individually todifierent x ones of said pressure chambers. r a. ,6. Drying apparatusaccording to-claim 3 comprising shaped ports in said intermediate wallbetween said manifoldand respective pressure chambers; movable shuttersrespeotivelyta'ssociated.with said ports; and means con- 2,012,115, 8/35Woodrutf "34-23 2,837,830 6/58 'Fry 34* '114 X 1 2,919,495 1/60 Underhay34l60 X 2,929,153 3/60 Fr 34' 114 X f ronnro'n PATENTS 727,058 3/55Great Britain. 7 1 773,908 5/57 Great'Britain;

fne cted to said shutters, respectively and beingro'perable 7 from theexterior of said enclosing casing.

, References'Cited by the-Examiner UNITED STATES PATENTS NORMANYUDKOFEPr'imary Examiner,

"GEORGE/D. MITCHELL, CHARLES OCONNELL,'

: j BENJAMIN BENDETT, Examine

1. A DRYING HOOD FOR A DRYING CYLINDER OF A MACHINE FOR DRYING SHEETMATERIAL IN CONTINUOUS LENGTHS TO BE ENTRAINED ABOUT SAID CYLINDER,COMPRISING A CASING HAVING LONGITUDINAL WALLS, TRANSVERSE WALLS, A TOPWALL AND A BOTTOM WALL, SAID BOTTOM WALL BEING AT LEAST IN PART OFEXTERIORLY CONCAVE ARCUATE SHAPE ADAPTED TO THE PERIPHERY OF THE DRYINGCYLINDER AND HAVING ITS AXIS SUBSTANTIALLY PARALLEL TO SAID TRANSVERSEWALLS; A MANIFOLD WITHIN SAID CASING, A SUPPLY CHAMBER BEING DEFINEDBETWEEN SAID TOP WALL AND SAID MANIFOLD; HEATING MEANS DISPOSED IN SAIDSUPPLY CHAMBER FOR HEATING GASEOUS MEDIUM THEREIN; FAN MEANS HOUSEDWITHIN SAID CASING AND HAVING ITS INLET IN SAID SUPPLY CHAMBER AND ITSOUTLET WITHIN SAID MANIFOLD FOR SUPPLYING HEATED GASEOUS MEDIUM FROMSAID SUPPLY CHAMBER TO WITHIN SAID MANIFOLD; TWO TRANSVERSE PARTITIONSPARALLEL RESPECTIELY TO THE TRANSVERSE WALLS AND EXTENDING FROM SAIDBOTTOM WALL TO SAID MANIFOLD ONE AT EACH SIDE OF SAID ARCUATE PART OFSAID BOTTOM WALL DEFINING A PATH FOR RETURN FLOW OF EXHAUST GAS TO THESUPPLY CHAMBER; LONGITUDINAL PARTITIONS EXTENDING BETWEEN SAIDTRANSVERSE PARTITIONS TO DEFINE A PLURALITY OF PRESSURE CHAMBERS BETWEENTHE BOTTOM OF THE MANIFOLD AND THE ARCUATE SURFACE, AND A PLURALITY OFEXHAUST PASSAGEWAYS COEXTENSIVE WITH THE PRESSURE CHAMBERS ABOUT THEPERIPHERY OF THE CYLINDER, THE FACE OF SAID MANIFOLD FACIONG SAID BOTTOMWALL BEING PROVIDED WITH PORTS FOR THE FLOW OF HEATED GASEOUS MEDIUMFROM THE INTERIOR OF SAID MANIFOLD TO EACH OF SAID PRESSURE CHAMBERS;SHUTTERS FOR CLOSING SAID PORTS TO A VARIABLE EXTENT, EACH OF SAIDSHUTTERS BEING INDIVIDUAL TO ONE OF SAID PRESSURE CHAMBERS; AND MEANSFOR INDIVIDUALLY ADJUSTING SAID SHUTTERS FROM WITHOUT SAID CASING, SAIDARCUATE PART OF SAID BOTTOM WALL BEING APERTURED FOR THE DIRECTION OFGASEOUS MEDIUM FROM SAID PRESSURE CHAMBERS ON TO A WEB OF PAPER ON SAIDDRYING CYLINDER AND FURTHER APERTURED TO PROVIDE ACCESS TO SAID EXHAUSTPASSAGEWAYS FOR GASEOUS MEDIUM FLOWING OVER AND AWAY FROM THE OUTERSURFACE OF SAID WEB ON SAID CYLINDER AND SAID EXHAUST PASSAGEWAYSCOMMUNICATING THROUGH SAID TRANSVERSE PARTITIONS WITH SAID SUPPLYCHAMBER FOR THE RETURN TO SAID SUPPLY CHAMBER OF GASEOUS MEDIUM RECEIVEDIN SAID EXHAUST PASSAGEWAYS.